The present invention relates generally to portable helical-scan video tape recorders, and more specifically to a circuit for controlling the angular velocity and angular position of video heads mounted on a rotary cylinder.
In video tape recorders, the angular velocity and angular position of video heads are precisely controlled by error signals which are derived by comparison between reference speed and position signals and actual speed and position signals, respectively, so that each video head may precisely trace intended tracks during both recording and playback modes. Because of the high degree of precision with which the rotary mechanism is constructed, the rotation of the heads is easily disturbed by an external shock. In cases where the recorder is of a compact portable type, such disturbances occur frequently, causing the angular position of the heads to deviate from the reference phase with a resultant deviation of heads from the intended track.
One approach is to employ a playback head to play back the recorded material immediately after it is recorded, so that the user is able to monitor the quality of the recording. However, this type of approach is not satisfactory to portable video tape recorders of modest price since it adds to the complexity of the rotary mechanism with a resultant increase in equipment size and cost.